S. II. SCUDDER ON PALAEOZOIC COCKROACHES. 



27 



PALAEOBLATTARIAE. 



Tribe I. Mylacridae. Branches of the mediastinal vein arranged in a radiate manner, mostly springing from a common 

 point at the base of the wing; mediastinal area subtriangular, uniformly tapering apically. (:i o-enera. American.) 



Wings broad. Mediastinal ami scapular areas together occupying less than half the wino-. Ex- 

 i ternomedian area tolerably large, expanding regularly beyond the first branch. 

 mediastinal vein arising ) Mylacris. (5 species). 



close to the base of the 



. . j Wings slender. Mediastinal ami scapular areas together occupying more than half the wino-. 



Externomedian area small and compressed, scarcely expanding apically. 



Lithotnylacris. (3 species.) 

 Some of the apical branches of the mediastinal vein arising beyond the base of the wing and scarcely partaking in I he 



Neeymylacris. (2 species.) 



radiate arrangement of the others. 



Tribe II. Blattinaxiae. Branches of the mediastinal vein arising at regular intervals from a principal stem; mediastinal 

 area generally band-shaped. (8 genera. Both worlds.) 



Internomedian vein termin- 

 ating beyond, rarely at, 

 the middle of the outer 

 half of the wing. Scapu- 

 lar and externomedian 

 areas together covering 

 less than one half of the 



/Mediastinal area compar- 

 atively short, rarely ex- 

 ceeding, seldom equalling 

 two-thirds the length of 

 the wing. 



Mediastinal area long, usu- 

 ally at least three-fourths 

 the length of the wing, 

 sometimes nearly reach- 

 ing the tip. 



Scapular area not reaching the tip of the wing, the extrem- 

 ity of the main vein curving upward. Externomedian 

 area comparatively large. 



Etoblattina. (20 species. Both worlds.) 



Scapular area extending beyond and embracing the tip of 

 the wing, by the backward sweep of the main vein. Ex- 

 ternomedian area comparatively small. 



Arehimylacris. (2 species. American.) 



Externomedian branches inferior, so 

 that the nervules divaricate on 

 either side uf the seapular-externo- 

 median interspace. Allthraco- 

 blattina. (7 species. European.) 



Branches of 

 scapular vein 

 superior. 



Externomedian branches superior, 

 so that the nervules divaricate on 

 either side of the externomedian- 

 internomedian interspace. 



Gerablat- 

 tina. (12 species. Both worlds.) 

 Branches of scapular vein inferior. 



Hermatoblattina. (2 species. European.) 



Internomedian vein termin- 

 ating before the middle of 

 the outer half of the wing. 

 Scapular and externo- 

 median areas together 

 covering more than half 

 the wing. 



Externomedian vein di- 

 rected toward and ter- 

 minating near the apex 

 of the wing, its branches 

 inferior. 



Principal veins closely crowded in the basal half of the 



wing. Branches uniformly distributed all over the wing. 



Scapular area terminating above the apex of the wing. 



Progonoblattina. (2 species. European.) 



Principal veins widely separated in the basal half of the 

 wing. Branches much more closely crowded in some 

 parts of the wing than in others. Scapular area termin- 

 ating below the apex of the wing. 



Oryctoblattina. (1 species. European.) 



Externomedian vein directed toward 

 \ °f the wing, its branches superior. 



terminating near the middle of the inner border 

 Petrablattina. (2 species. Both worlds.) 



